Introduction to Trilaminar Embryology Flashcards
What is competence and what does it require?
- Capacity of responder cells to respond to induction
- Requires activation of responding tissue by competence factor
What are the two functions. of the cortex of the ovary?
- OOGENESIS
- FOLLICULOGENESIS
Describe follicle maturation.
- Essential for ovulation
- Caused by surge in FSH
Describe the appearance of follicle cells.
PRIMORDIAL FOLLICLE - squamous
PRIMARY FOLLICLE - cuboidal
LATE PRIMARY - stratified
What occurs in phase 1 of fertilisation?
- Capacitation of sperm
- Glycoprotein coat and plasma membrane proteins removed from acrosomal region
- Penetration of corona radiata
What occurs in phase 2 of fertilisation? PART 1
- Sperm binds to zona pellucida
- Release of acrosin and trypsin
What occurs in phase 2 of fertilisation? PART 2
- Once head of sperm breaks through zona pellucida, enzymes released from oocyte plasma membrane
- Enzymes alter properties of zona pellucida, prevent entry of any other sperm
Describe phase 3 of fertilisation.
- Sperm leaves plasma membrane on oocyte surface. Male pronucleus forms.
- Oocyte completes 2nd meiotic divsion to form 2nd polar body. Female pronucleus forms
- Pronuclei fuse
What occurs around day 6?
- Capture of blastocyst from uterine cavity
- L-selectins attach to carbohydrate receptors on uterine epithelium.
- Trophoblast integrins stimulate laminin and fibronectin development - causes further implantation
What are some abnormal sites of implantation and what are the consequences?
- Abdominal cavity, ovary and fallopian tube
- Can cause ectopic/extrauterine pregnancy
What occurs in day 9?
- Blastocyst deeply buried in endometrium
- Flattened hypoblast cells form Heuser’s membrane which lines exocoelomic cavity/primitive yolk sac
- Vacuoles form lacunae in syncytium
What occurs in days 11-12? PART 1
- Blastocyst completely embedded
- Syncytiotrophoblast cells erode congested maternal capillaries
What occurs in days 11-12? PART 2
- Lacunae become continuous with sinusoids
- Maternal blood enters lacunar system - uteroplacental circulation
What occurs in days 15-16?
- Primitive streak present on surface of epiblast
- Primitive node develops at cephalic end of streak
- Epiblastic cell invaginate through streak - using FGF8
What is the notochord?
- Formed in cranial region and develops caudally
- Signalling centre for FGF, TGF and Wnt
Describe development of the notochord.
- Pre-notochordal cells invaginate through primitive streak and embed in endoderm
- Cells proliferate and detach from endoderm
Describe anterior-posterior body axis establishment.
- Migration of AVE cells to cranial end of endoderm
- Express genes for head formation
Describe dorso-ventral body axis formation.
- Maintained by transcription factor - Nodal
- Regulates body axis formation with other transcription factors
Describe left-right body axis establishment.
- FGF8 controls Nodal - restricted to left side
- Left differentiated from right
Describe trophoblast development. PART 1
- Extraembryonic mesodermal cells penetrate core of primary villi - secondary villus
- Differentiate into blood cells - tertiary villus
Describe trophoblast development. PART 2
- Capillaries in tertiary villi make contact with capillaries in mesoderm of connecting stalk
- Capillaries in extraembryonic mesoderm make contact with intraembryonic vessels
